1. Field of the Invention
The present invention relates to a fan assembly and more particularly to a composite blade assembly and coupling elements for adjustably securing the blade assemblies in different pitch positions.
2. Description of the Prior Art
Propellers and blades which rotate at relatively high speeds are subjected to not only centrifugal forces but also shear forces, bending moments and repeated loadings at different levels which may result in fatigue failures. In addition, the rotating propellers are subjected to stress concentrations resulting from material imperfections and/or discontinuities in the elements, such as notches or holes, which may result in a fracture or failure of the material at the imperfection or discontinuity. Accordingly, there has been a trend to develop propellers of a lightweight strong material, such as aluminum or the like, and connect the propellers to a rotor or hub assembly with adequate, efficient connections.
Propellers which include coupling elements for securing propeller blades to a rotor hub are generally disclosed in U.S. Pat. Nos. 1,816,317, 1,862,328, 1,865,170, 2,289,400, and 2,350,345. Further, U.S. Pat. No. 3,461,966 discloses another type of propeller assembly which incorporates a continuous propeller blade constructed of a lightweight material such as aluminum. Propellers which include integral mounting flanges adapted to be disposed between mounting members are generally disclosed in U.S. Pat. Nos. 1,771,365 and 2,542,251.
Fan apparatus comprising a rotor, a plurality of fan blades and coupling means for securing the fan blades to the rotor, have been manufactured and described in the literature. For example, LAU Industries Incorporated of Dayton, Ohio make LAU ring fans incorporating extruded blades that are welded to cast hubs. Further, Western Engineering and Mfg. Co. of Marina Del Rey, California has produced aluminum alloy cast blades, under the name Valkyrie propellers, provided with cylindrical grooved shanks permitting the blades to be adjustably secured to a cast or the like rotor at desired pitch position. Additionally, American Coolair Corporation of Jacksonville, Florida, has manufactured propeller fans which include extruded aluminum blades fastened to cast clamshell members which, in turn, are fastened to a cast rotor. Although extruded blades are widely used as fan blades, problems have been encountered in connecting the extruded blades to mounting members with bolts, rivets or like fasteners and adjustably connecting the mounting members and blade to a rotor.
For various blade assemblies wherein a fan blade is connected to a mounting member with bolts, rivets or similar clamping elements, it is preferable to form a friction type connection between the fan blade and mounting member to preclude performance problems such as fatigue effects resulting from stress reversals, stress fluctuations and stress discontinuities. However, with friction-type connections the frictional resistance is proportional to the clamping force of the fasteners and a yielding of the fasteners often results in a partial bearing-type connection wherein the loading effects of stress fluctuations, stress discontinuities (eg. resulting from holes or notches) and stress concentrations tend to have a more pronounced adverse effect on the behavior of the connection. Accordingly, the fan apparatus and blade assemblies built according to the present invention are designed to overcome problems, such as fatigue failure, encountered with other prior art.